Performance analysis of vapor-cooled shield insulation integrated with para-ortho hydrogen conversion for liquid hydrogen tanks

A composite thermal insulation system consisting of variable-density multi-layer insulation (VDMLI) and vapor-cooled shields (VCS) integrated with para-ortho hydrogen (P-O) conversion is proposed for long-term storage of liquid hydrogen. High-performance thermal insulation is realized by minimizing the thermal losses via the VDMLI design and fully recovering the cold energy released from the sensible heat and P-O conversion of the vented gas. Effects of different design considerations on the thermal insulation performance are studied. The results show that the maximum reduction of the heat leak with multiple VCSs can reach 79.9% compared to that without VCS. The heat leak with one VCS is reduced by 61.1%, and further reduced by 11.6% after adding catalysts. It is found that the deterioration of the insulation performance has an almost linear relationship with catalytic efficiency. A unified criterion with relative optimization efficiency is finally proposed to evaluate the improvement of the VCS number.     

Variations of methane conversion process with the geometrical effect in rotating gliding arc reactor

Controllability of the kinetic path of methane conversion in plasma driven oxidation reaction is investigated. Different geometries in a rotating gliding arc reactor are adopted to control reaction paths in methane oxidation reaction. Diverging and converging type reactor product different reaction environments in view point of both the reaction time and the degree of thermal activation. In the diverging reactor, the partial oxidation process is dominant with high methane conversion because the diverging section facilitates to elongate the arc length and decrease the flow velocity. Thus, the convective and radiative heat transfer from the arc column to the reactants could be enhanced. The role of plasma in the diverging reactor is mainly igniting and sustaining the partial oxidation, which is rather different from that in the converging reactor where the plasma plays as a heat source for thermal pyrolysis of methane with the help of focusing thermal energy of the arc.     

Significance of ortho-para hydrogen conversion in the performance of hydrogen liquefaction process

Hydrogen is an energy vector and is produced just like electricity. In order to overcome the shortcomings associated with its low molecular weight and energy density per unit volume, hydrogen is liquefied for storage and transportation purposes. The liquefaction of hydrogen differs from that of other substances as it involves the reactive transformation of its isomeric states. At 25 °C, molecular hydrogen consists of 75% orthohydrogen and 25% of parahydrogen. As the normal boiling point, hydrogen essentially exists in the para-state, which is preferred because of its lower boil-off gas rate. However, the conversion of ortho-to-para hydrogen is an exothermic reaction, and this enthalpy of conversion enhances the total reversible work by about 15%. Little work has been done regarding ortho-to-para hydrogen conversion from the process systems point of view. Therefore, parametric analysis of this vital conversion reaction was studied with potential impact on the performance of cryogenic heat exchangers, reactors configuration and mode of operation, and probable impact on the energy efficiency of the liquefaction process. An alternate approach to simulate the reaction is also proposed. The results show that the current approaches to process design need to be changed. The study opens avenues for more in-depth analysis and optimization approaches to present a holistic framework for future integrated energy systems.     

Molecular simulation of copper based metal-organic framework (Cu-MOF) for hydrogen adsorption

Metal organic framework (MOF) are widely used in adsorption and separation due to their porous nature, high surface area, structural diversity and lower crystal density. Due to their exceptional thermal and chemical stability, Cu-based MOF are considered excellent hydrogen storage materials in the world of MOFs. Efforts to assess the effectiveness of hydrogen storage in MOFs with molecular simulation and theoretical modeling are crucial in identifying the most promising materials before extensive experiments are undertaken. In the current work, hydrogen adsorption in four copper MOFs namely, MOF-199, MOF 399, PCN-6′, and PCN-20 has been analyzed. These MOFs have a similar secondary building unit (SBU) structure, i.e., twisted boracite (tbo) topology. The Grand Canonical Monte Carlo (GCMC) simulation was carried at room temperature (298 K) as well as at cryogenic temperature (77 K) and pressures ranging from 0 to 1 bar and 0–50 bar. These temperatures and pressure were selected to comply with the conditions set by department of energy (DOE) and to perform a comparative study on hydrogen adsorption at two different temperatures. The adsorption isotherm, isosteric heat, and the adsorption sites were analyzed in all the MOFs. The findings revealed that isosteric heat influenced hydrogen uptake at low pressures, while at high pressures, porosity and surface area affected hydrogen storage capacity. PCN-6′ is considered viable material at 298 K and 77 K due to its high hydrogen uptake.     

Study on performance comparison of different fin combinations of catalyst filled plate fin heat exchanger for hydrogen liquefaction

A mathematical model of catalyst filled plate fin heat exchanger (CFPFHE) is established to compare different fin models and analyze fin performance of different fin combinations. The results show that the single-layer fin model inadequately reflects the double-layers fin model from flow distribution and fin performance. The indexes of ortho-para hydrogen conversion (YY_pH2) of different fin combinations are all about 0.95, meeting the requirement of the CFPFHE. The plain_serrated fin has the best fin performance among four fin combinations. Compared with the plain_plain, the Colburn heat transfer factor (j factor) and thermal enhancement factor (TEF) of cool and hot sides of the plain_serrated fin are increased by 68.0～51.0% and 28.5～13.6%, 8.5～6.1% and 8.4%～6.1% at Re_hot = 500～1500, respectively. Further, the fin combinations of high-efficiency fin and plain respectively used in cool and hot sides have excellent overall fin performance, which provides a theoretical guidance for fin selection of the CFPFHE.     

Review of hydrogen economy in Malaysia and its way forward

Heavy fossil fuels consumption has raised concerns over the energy security and climate change while hydrogen is regarded as the fuel of future to decarbonize global energy use. Hydrogen is commonly used as feedstocks in chemical industries and has a wide range of energy applications such as vehicle fuel, boiler fuel, and energy storage. However, the development of hydrogen energy in Malaysia is sluggish despite the predefined targets in hydrogen roadmap. This paper aims to study the future directions of hydrogen economy in Malaysia considering a variety of hydrogen applications. The potential approaches for hydrogen production, storage, distribution and application in Malaysia have been reviewed and the challenges of hydrogen economy are discussed. A conceptual framework for the accomplishment of hydrogen economy has been proposed where renewable hydrogen could penetrate Malaysia market in three phases. In the first phase, the market should aim to utilize the hydrogen as feedstock for chemical industries. Once the hydrogen production side is matured in the second phase, hydrogen should be used as fuel in internal combustion engines or burners. In the final phase hydrogen should be used as fuel for automobiles (using fuel cell), fuel-cell combined heat and power (CHP) and as energy storage.     

Biomass gasification coupled with producer gas cleaning,bottling and HTS catalyst treatment for H2-rich gas production

The aim of the present study is to demonstrate the production of hydrogen-rich fuel gas from J. curcas residue cake. A comprehensive experimental study for the production of hydrogen rich fuel gas from J. curcas residue cake via downdraft gasification followed by high temperature water gas shift catalytic treatment has been carried out. The gasification experiments are performed at different equivalence ratios and performance of the process is reported in terms of producer gas composition & its calorific value, gas production rate and cold gas efficiency. The producer gas is cleaned of tar and particulate matters by passing it through venturi scrubber followed by sand bed filter. The clean producer gas is then compressed at 0.6 MPa and bottled into a gas cylinder. The bottled producer gas and a simulated mixture of producer gas are then subjected to high temperature shift (HTS) catalytic treatment for hydrogen enriched gas production. The effect of three different operating parameters GHSV, steam to CO ratio and reactor temperature on the product gas composition and CO conversion is reported. From the experimental study it is found that, the presence of oxygen in the bottled producer gas has affected the catalyst activity. Moreover, higher concentration of oxygen concentration in the bottled producer gas leads to the instantaneous deactivation of the HTS catalyst.     

Superior anti-impurity gas poisoning ability and hydrogen storage properties of Ti–Cr alloy by introducing zirconium as additive

In this work, the anti-impurity gas poisoning ability and hydrogen storage properties of Ti–Cr alloy by introducing zirconium as additive have been investigated. The results showed that all alloys had C14-type main phase and Ti minor phase. The lattice parameter a, c and cell volume of the C14-type phase rose as Zr content increased. Furthermore, after introducing Zr, all alloys could absorb hydrogen immediately without any prior heat treatment or hydrogen exposure with/without prolonged air exposure. The maximum hydrogen storage capacity and the average effective hydrogen storage capacity of TiCr₂ alloy also increased with Zr content. The cycle properties of all alloys with/without prolonged air exposure were also discussed. The results showed that all alloys had good cycle stability even if the alloys were exposed to the air for 2 days. The above results suggested that the addition of Zr had a positive effect on improving the hydrogen storage properties and anti-impurity gas poisoning properties of TiCr₂ alloy. Finally, the mechanisms of first hydrogenation kinetic of all alloys with/without prolonged air exposure were also investigated by using the rate limiting step.     

A novel approach to ammonia synthesis from hydrogen sulfide

There are a number of shortcomings for currently-available technologies for ammonia production, such as carbon dioxide emissions and water consumption. We simulate a novel model for ammonia production from hydrogen sulfide through membrane technologies. The proposed production process decreases the need for external water and reduces the physical footprint of the plant. The required hydrogen comes from the separation of hydrogen sulfide by electrochemical membrane separation, while the required nitrogen is obtained from separating oxygen from air through an ion transport membrane. 10% of the hydrogen from the electrochemical membrane separation along with the separated oxygen from the ion transport membrane is sent to the solid oxide fuel cell for heat and power generation. This production process operates with a minimal number of processing units and in physical, kinetic, and thermal conditions in which a separation factor of ~99.99% can be attained.     

CuWO4 as a novel Z-scheme partner to construct TiO2 based stable and efficient heterojunction for photocatalytic hydrogen generation

Synthesis of highly efficient, stable, visible active CuWO₄ nanoparticles through a simple methodology, paves a feasible path for enhancing the efficiency of TiO₂. A novel nanocomposite of CuWO₄ NP loaded TiO₂ NR heterojunction was mounted through a direct Z-scheme mechanism. Optimized composite CWT-3, advances the photocatalytic hydrogen production rates of TiO₂ to 106.7 mmol h^?1 g^?1_cat. CuWO₄ incorporation as OEP compensates inefficiency of WO₃ and other Z-scheme combinations reported so far, on limiting the charge carrier recombination followed by the generation of a greater number of excitons. Specific amounts of catalyst loading, study on the effect of sacrificial reagents, and understanding the effect of the light source, are the three pivotal steps that helped here to hamper the density of overall back reactions. The formation of Z-scheme heterojunction was evidently confirmed on determining the position of CBM and VBM, PL and photoelectrochemical analysis. Recyclability studies further proved the stable and efficient outcomes of CWT-3 for five consecutive cycles. Based on photocatalytic activity, employing BDF by-product glycerol as an optimized sacrificial reagent serves the oxidation demands and triggered 53.26% solar to hydrogen conversion efficiency under natural sunlight irradiation.     

Hydrogen-rich syngas production by gasification of Urea-formaldehyde plastics in supercritical water

Supercritical water is a promising medium to convert plastics into hydrogen and other recyclable products efficiently. In previous research, supercritical water gasification characteristics investigations focus on thermoplastics instead of thermoset plastics due to its chemical, thermal and mechanical stability. Urea-formaldehyde (UF) plastics were selected as a typical kind of thermoset plastics for investigation in this paper and quartz tubes were used as the reactor in order to avoid the potential catalytic effect of metal reactor wall. Conversion characteristic were studied and the influence of different operating parameters such as temperature, reaction time, feedstock mass fraction and pressure were investigated respectively. The molar fraction of hydrogen could reach about 70% in 700 °C. Products in gas phase and solid phase were analyzed, and properties, chemical structures and inhibition mechanism of thermoset plastics was analyzed after comparing with polystyrene (PS) plastics. The result showed that increase of high temperature and long reaction time could promote gasification process, meanwhile the increase in the feedstock mass fraction would result in suppression of the gasification process. Finally, kinetic study of UF was carried out and the activation energy and pre-exponential factor of the Arrhenius equation were calculated as 30.09 ± 1.62 kJ/mol and 0.1199 ± 0.0049 min⁻¹, respectively.     

Effect of welding process parameters on embrittlement of Grade P92 steel using Granjon implant testing of welded joints

Precipitation of Cr-rich carbides, diffusible hydrogen content and heterogeneous microstructure formation across the weldments makes heat-affected zone (HAZ) susceptible to intergranular cracking and makes weldability of creep strength enhanced ferritic (CSEF) Grade P92 steel a critical issue. In the present research work, the Granjon implant test and mercury method (for diffusible hydrogen measurement) have been performed on Grade P92 steel welded specimens to study the effect of welding parameters on diffusible hydrogen levels and their subsequent effect on hydrogen-assisted cracking (HAC). The weld metal was deposited by a shielded metal arc welding process on Grade P92 steel samples using P92 matching filler. The three different welding conditions are used to measure the diffusible hydrogen level in the deposited metal. Granjon implant test was performed to evaluate HAZ HAC susceptibility with similar welding conditions which were used in the mercury method. Lower critical stress (LCS) was also evaluated using the Granjon implant test. The higher susceptibility of CSEF Grade P92 steel welded plate towards HAZ HAC was noticed in case of lower heat input or higher diffusible hydrogen content. However, by considering LCS, fracture mode and diffusible hydrogen content, the weld deposited using the highest heat input (condition III) offers great resistance to HAZ HAC.     

Numerical study on unsteady characteristics of high-pressure hydrogen jet ejected from a pinhole

The aim of this study was to delineate the unsteady fluid dynamics of the high-pressure hydrogen jet to clarify the relationship between the forced ignition position and the flame development characteristics in a high-pressure hydrogen jet leaking from a pinhole. The Navier–Stokes equation for a compressible multi-component gas was used to simulate a high-pressure (82 MPa stagnation pressure) unsteady hydrogen jet ejected into the atmosphere through a pinhole (diameter = 0.2 mm). The results indicated that the flapping jet at the base of the jet formed a cloud of highly concentrated hydrogen that flowed downstream. A correlation was observed between the spatio-temporal distribution of hydrogen concentration and velocity was observed. The unsteady high-pressure hydrogen jet obtained by simulation will be used in subsequent studies focusing on flame development under forced ignition.     

A review on current trends in potential use of metal-organic framework for hydrogen storage

Hydrogen can be a promising clean energy carrier for the replenishment of non-renewable fossil fuels. The set back of hydrogen as an alternative fuel is due to its difficulties in feasible storage and safety concerns. Current hydrogen adsorption technologies, such as cryo-compressed and liquefied storage, are costly for practical applications. Metal-organic frameworks (MOFs) are crystalline materials that have structural versatility, high porosity and surface area, which can adsorb hydrogen efficiently. Hydrogen is adsorbed by physisorption on the MOFs through weak van der Waals force of attraction which can be easily desorbed by applying suitable heat or pressure. The strategies to improve the MOFs surface area, hydrogen uptake capacities and parameters affecting them are studied. Hydrogen spill over mechanism is found to provide high-density storage when compared to other mechanisms. MOFs can be used as proton exchange membranes to convert the stored hydrogen into electricity and can be used as electrodes for the fuel cells. In this review, we addressed the key strategies that could improve hydrogen storage properties for utilizing hydrogen as fuel and opportunities for further growth to meet energy demands.     

Effect of high compression ratio on improving thermal efficiency and NOx formation in jet plume controlled direct-injection near-zero emission hydrogen engines

The Plume Ignition and Combustion Concept (PCC) developed by the authors significantly reduced nitrogen oxide (NOx) emissions in a direct-injection hydrogen engine under high-load operation. With PCC, a rich fuel plume is ignited immediately after completion of injection in the latter half of the compression stroke to reduce NOx formation. Simultaneously, high thermal efficiency was also achieved by mitigating cooling losses through optimization of the jet configuration in the combustion chamber. This basic combustion concept was applied to burn lean mixture in combination with the optimized hydrogen jet configuration and the application of supercharging to recover the power output decline due to the use of a diluted mixture. As a result, a near-zero-emission-level engine has been achieved that simultaneously provides high thermal efficiency, high power output and low NOx emissions at a single-digit ppm level [1]. In this study, a high compression ratio was applied to improve thermal efficiency further by taking advantage of the characteristics of hydrogen fuel, especially its diluted mixture with a high anti-knock property. As a result, NOx emissions at a single-digit ppm level and gross indicated thermal efficiency of 52.5% were achieved while suppressing knocking at a compression ratio of 20:1 by optimizing the excess air ratio and injection timing, and increasing power output by supercharging.     

Performance analysis of metal hydride based simultaneous cooling and heat transformation system

The performance of metal hydrides based simultaneous cooling and heat transformation system (MHCHT) using a combination of La_0.9Ce_0.1Ni₅–MmNi_4.4Al_0.6–MmNi_3.7Co_0.7Mn_0.3Al_0.3 hydrides is evaluated. The MHCHT is thermodynamically analysed using statically and dynamically measured PCIs and thermodynamic properties. In addition, a set of governing equations is solved in order to study the heat and hydrogen transfer between the reaction beds. The experimental PCI measurement data are compared with the numerical results and a reasonably good agreement is observed between them. From the results, the slope and hysteresis factors are determined for further thermal analyses. It is observed that the performance parameters i.e. cooling capacity, heat transformation capacity and coefficient of performance (COP) of MHCHT are significantly decreased by 42.4%, 26.7% and 19.1% respectively when dynamic property data are considered compared to static property data. In addition, the thermodynamic cycle is analysed by considering the variation in pressure during hydrogen transfer process between the metal hydride beds.     

Effect of introducing manganese as additive on microstructure,hydrogen storage properties and rate limiting step of Ti–Cr alloy

TiCr₂ with adding different amount of Mn (0, 2, 4 and 8 wt.%) alloys have been investigated. All alloys have C14-type main phase (gray color in SEM) and Ti minor phase (dark gray color in SEM). Rietveld fitting results proved that the lattice parameter a and cell volume of C14-type phase decreased with increasing Mn content. The first hydrogenation measurement manifest that all alloys have best activation properties and could be activated without any prior heat treatment and hydrogen exposure. However, introducing Mn led to the decrease of the first hydrogen absorption rate of TiCr₂ alloy, which may be due to the decrease of cell volume of C14-type main phase. The first hydrogenation properties at low temperature and effect of air exposure of the alloy were discussed. The results showed that the maximum hydrogen absorption capacity at 0 °C was obviously higher than that at room temperature. In addition, TiCr₂ alloy doped with minor amounts of Mn after long-time air exposure showed better hydrogenation performance. This may be due to the Mn additive acting as a deoxidizer. Finally, the first hydrogenation kinetic mechanisms of all alloys at different temperature were also studied by using the rate limiting step.     

Refueling-station costs for metal hydride storage tanks on board hydrogen fuel cell vehicles

Refueling costs account for much of the fuel cost for light-duty hydrogen fuel-cell electric vehicles. We estimate cost savings for hydrogen dispensing if metal hydride (MH) storage tanks are used on board instead of 700-bar tanks. We consider a low-temperature, low-enthalpy scenario and a high-temperature, high-enthalpy scenario to bracket the design space. The refueling costs are insensitive to most uncertainties. Uncertainties associated with the cooling duty, coolant pump pressure, heat exchanger (HX) fan, and HX operating time have little effect on cost. The largest sensitivities are to tank pressure and station labor. The cost of a full-service attendant, if the refueling interconnect were to prevent self-service, is the single largest cost uncertainty. MH scenarios achieve $0.71–$0.75/kg-H₂ savings by reducing compressor costs without incurring the cryogenics costs associated with cold-storage alternatives. Practical refueling station considerations are likely to affect the choice of the MH and tank design.     

Energy efficient hydrogen drying and purification for fuel cell vehicles

High-purity standards are required for hydrogen used in fuel cell vehicles. The relative abundance of contaminants is highly influenced by the production pathway. Hydrogen obtained from water electrolysis presents three main pollutants: Nitrogen, Oxygen and Water. Herein, the engineering and implementation of removal techniques in a commercial 50 kW alkaline electrolyzer are reported. The full system was characterized with various analytical techniques including gas chromatography and mass spectrometry. A reduction of contaminant levels compatible with ISO 14687:2019 standard was achieved. From cold start, 100 min of operation are required to reach the desired nitrogen levels. Oxygen was removed in one step with a catalytic converter. Drying of hydrogen was achieved by using an innovative vacuum assisted pressure swing adsorption system. Sub-ppm levels of water are obtained with a power consumption of only 0.5 kWh/kg H₂ and 98.4% of product recovery.     

Design and computational analysis of a metal hydride hydrogen storage system with hexagonal honeycomb based heat transfer enhancements-part A

In this study, design and performance analysis is carried out for a 10 kWh metal hydride based hydrogen storage system. The system is equipped with distinctive aluminium hexagonal honeycomb based heat transfer enhancements (HTE) having higher surface area to volume ratio for effective heat transfer combined with low system weight addition. The system performance was studied under different operating conditions. The optimum absorption condition was achieved at 35 bar with water at room temperature as heat transfer fluid where up to 90% absorption was completed in 7200 s. The performance of the reactor was observed to significantly improve upon the addition of the HTE network at a minimal system weight penalty.